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  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
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  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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  • H01M4/00—Electrodes
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  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
  • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
• • H—ELECTRICITY
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  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
• • H—ELECTRICITY
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  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/621—Binders
  • H01M4/622—Binders being polymers
  • H01M4/623—Binders being polymers fluorinated polymers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• This invention relates to improved materials usable as electrode active materials and to their preparation.
• Lithium batteries are prepared from one or more lithium electrochemical cells containing electrochemically active (electroactive) materials. Such cells typically include an anode (negative electrode), a cathode (positive electrode), and an electrolyte interposed between spaced apart positive and negative electrodes. Batteries with anodes of metallic lithium and containing metal chalcogenide cathode active material are known.
• the electrolyte typically comprises a salt of lithium dissolved in one or more solvents, typically nonaqueous (aprotic) organic solvents.
• Other electrolytes are solid electrolytes typically called polymeric matrixes that contain an ionic conductive medium, typically a metallic powder or salt, in combination with a polymer that itself may be tonically conductive which is electrically insulating.
• lithium metal anode such as a lithium metal chalcogenide or lithium metal oxide.
• Carbon anodes such as coke and graphite, are also insertion materials.
• Such negative electrodes are used with lithium-containing insertion cathodes, in order to form an electroactive couple in a cell.
• Such cells in an initial condition, are not charged.
• In order to be used to deliver electrochemical energy such cells must be charged in order to transfer lithium to the anode from the lithium-containing cathode. During discharge the lithium is transferred from the anode back to the cathode. During a subsequent recharge, the lithium is transferred back to the anode where it re-inserts.
• lithium ions Li +
• Such rechargeable batteries having no free metallic species are called rechargeable ion batteries or rocking chair batteries. See U.S. Pat. Nos. 5,418,090; 4,464,447; 4,194,062; and 5,130,211.
• Preferred positive electrode active materials include LiCoO 2 , LiMn 2 O 4 , and LiNiO 2 .
• the cobalt compounds are relatively expensive and the nickel compounds are difficult to synthesize.
• a relatively economical positive electrode is LiMn 2 O 4 , for which methods of synthesis are known.
• the lithium cobalt oxide (LiCoO 2 ), the lithium manganese oxide (LiMn 2 O 4 ), and the lithium nickel oxide (LiNiO 2 ) all have a common disadvantage in that the charge capacity of a cell comprising such cathodes suffers a significant loss in capacity.
• the initial capacity available (amp hours/gram) from LiMn 2 O 4 , LiNiO 2 , and LiCoO 2 is less than the theoretical capacity because significantly less than 1 atomic unit of lithium engages in the electrochemical reaction.
• Such an initial capacity value is significantly diminished during the first cycle operation and such capacity further diminishes on every successive cycle of operation.
• LiNiO 2 and LiCoO 2 only about 0.5 atomic units of lithium is reversibly cycled during cell operation.
• alkali transition metal oxide compounds suffer from relatively low capacity. Therefore, there remains the difficulty of obtaining a lithium-containing electrode material having acceptable capacity without disadvantage of significant capacity loss when used in a cell.
• the invention provides novel lithium-mixed metal materials which, upon electrochemical interaction, release lithium ions, and are capable of reversibly cycling lithium ions.
• the invention provides a rechargeable lithium battery which comprises an electrode formed from the novel lithium-mixed metal materials.
• Methods for making the novel lithium-mixed metal materials and methods for using such lithium-mixed metal materials in electrochemical cells are also provided.
• the lithium-mixed metal materials comprise lithium and at least one other metal besides lithium.
• Preferred materials are lithium-mixed metal phosphates which contain lithium and two other metals besides lithium.
• the invention provides a rechargeable lithium battery which comprises an electrolyte; a first electrode having a compatible active material; and a second electrode comprising the novel materials.
• the novel materials are lithium-mixed metal phosphates which preferably used as a positive electrode active material, reversibly cycle lithium ions with the compatible negative electrode active material.
• the lithium-mixed metal phosphate is represented by the nominal general formula Li a MI b MII c (PO 4 ) d .
• Such compounds include Li 1 MI a MII b PO 4 and Li 3 MI a MII b (PO 4 ) 3 ; therefore, in an initial condition 0 ⁇ a ⁇ 1 or 0 ⁇ a ⁇ 3, respectively.
• x quantity of lithium is released where 0 ⁇ x ⁇ a.
• the sum of b plus c is up to about 2. Specific examples are Li 1 MI 1-y MII y PO 4 and Li 3 MI 2-y MII y (PO 4 ) 3 .
• MI and MII are the same. In a preferred aspect, MI and MII are different from one another. At least one of MI and MII is an element capable of an oxidation state higher than that initially present in the lithium-mixed metal phosphate compound. Correspondingly, at least one of MI and MII has more than one oxidation state in the phosphate compound, and more than one oxidation state above the ground state M 0 .
• oxidation state and valence state are used in the art interchangeably.
• both MI and MII may have more than one oxidation state and both may be oxidizable from the state initially present in the phosphate compound.
• MII is a metal or semi-metal having a +2 oxidation state, and is selected from Groups 2, 12 and 14 of the Periodic Table.
• MII is selected from non-transition metals and semi-metals.
• MII has only one oxidation state and is nonoxidizable from its oxidation state in the lithium-mixed metal compound.
• MII has more than one oxidation state.
• MII is selected from Mg (magnesium), Ca (calcium), Zn (zinc), Sr (strontium), Pb (lead), Cd (cadmium), Sn (tin), Ba (barium), and Be (beryllium), and mixtures thereof.
• MII is a metal having a +2 oxidation state and having more than one oxidation state, and is oxidizable from its oxidation state in lithium-mixed metal compound.
• MI is selected from Fe (iron), Co (cobalt), Ni (nickel), Mn (manganese), Cu (copper), V (vanadium), Sn (tin), Ti (titanium), Cr (chromium), and mixtures thereof.
• MI is preferably selected from the first row of transition metals and further includes tin, and MI preferably initially has a +2 oxidation state.
• the product LiMI 1-y MII y PO 4 is an olivine structure and the product Li 3 MI 1-y (PO 4 ) 3 is a rhombohedral or monoclinic Nasicon structure.
• the term “nominal formula” refers to the fact that the relative proportion of atomic species may vary slightly on the order of 2 percent to 5 percent, or more typically, 1 percent to 3 percent.
• any portion of P (phosphorous) may be substituted by Si (silicon), S (sulfur), and/or As (arsenic); and any portion of O (oxygen) may be substituted by halogen, preferably F (fluorine).
• the metal phosphates are alternatively represented by the nominal general formulas such as Li 1-x MI 1-y MII y PO 4 (0 ⁇ 1), and Li 3-x MI 2-y MII y (PO 4 ) 3 signifying capability to release and reinsert lithium.
• the term “general” refers to a family of compounds, with M, x and y representing variations therein.
• the expressions 2-y and 1-y each signify that the relative amount of MI and MII may vary.
• MI may be a mixture of metals meeting the earlier stated criteria for MI.
• MII may be a mixture of metallic elements meeting the stated criteria for MII.
• MII is a mixture of 2 metallic elements; and where MI is a mixture, it is a mixture of 2 metals.
• each such metal and metallic element has a +2 oxidation state in the initial phosphate compound.
• the present invention provides a method of preparing a compound of the nominal general formula Li a MI b MII c (PO 4 ) d where 0 ⁇ a ⁇ 3; the sum of b plus c is greater than zero and up to about 2; and 0 ⁇ d ⁇ 3.
• Preferred compounds include Li 3 MI b MII c (PO 4 ) 3 where b plus c is about 2; and LiMI b MII c PO 4 where b plus c is about 1.
• the method comprises providing starting materials in particle form.
• the starting (precursor) materials include a lithium-containing compound, one or more metal containing compounds, a compound capable of providing the phosphate (PO 4 ) ⁇ 3 anion, and carbon.
• the starting materials are intimately mixed and then reacted together where the reaction is initiated by heat and is preferably conducted in a nonoxidizing, inert atmosphere, whereby the lithium, metal from the metal compound(s), and phosphate combine to form the Li a MI b MII c (PO 4 ) d product.
• the particles are intermingled to form an essentially homogeneous powder mixture of the precursors.
• the precursor powders are dry-mixed using a ball mill, such as zirconia media. Then the mixed powders are pressed into pellets.
• the precursor powders are mixed with a binder. The binder is selected so as to not inhibit reaction between particles of the powders.
• preferred binders decompose or evaporate at a temperature less than the reaction temperature.
• examples include mineral oils (i.e., glycerol, or C-18 hydrocarbon mineral oil) and polymers which decompose (carbonize) to form a carbon residue before the reaction starts, or which evaporate before the reaction starts.
• intermingling is conducted by forming a wet mixture using a volatile solvent and then the intermingled particles are pressed together in pellet form to provide good grain-to-grain contact.
• the precursor compounds be present in a proportion which provides the stated general formula of the product
• the lithium compound may be present in an excess amount on the order of 5 percent excess lithium compared to a stoichiometric mixture of the precursors.
• the carbon may be present at up to 100% excess compared to the stoichiometric amount.
• the method of the invention may also be used to prepare other novel products, and to prepare known products.
• lithium hydroxide melts at about 400° C. At some reaction temperatures preferred herein of over 450° C. the lithium hydroxide will melt before any significant reaction with the other precursors occurs to an effective extent. This melting renders the reaction very difficult to control.
• anhydrous LiOH is highly hygroscopic and a significant quantity of water is released during the reaction. Such water needs to be removed from the oven and the resultant product may need to be dried.
• the solid state reaction made possible by the present invention is much preferred since it is conducted at temperatures at which the lithium-containing compound reacts with the other reactants before melting.
• lithium hydroxide is useable as a precursor in the method of the invention in combination with some precursors, particularly the phosphates.
• the method of the invention is able to be conducted as an economical carbothermal-based process with a wide variety of precursors and over a relatively broad temperature range.
• the aforesaid precursor compounds are generally crystals, granules, and powders and are generally referred to as being in particle form.
• phosphate salts many types are known, it is preferred to use diammonium hydrogen phosphate (NH 4 ) 2 HPO 4 (DAHP) or ammonium dihydrogen phosphate (NH 4 )H z PO 4 (ADHP). Both ADHP and DAHP meet the preferred criteria that the precursors decompose in the presence of one another or react with one another before melting of such precursor.
• Exemplary metal compounds are Fe 2 O 3 , Fe 3 O 4 , V 2 O 5 , VO 2 , LiVO 3 , NH 4 VO 3 , Mg(OH) 2 , Cao, MgO, Ca(OH) 2 , MnO 2 , Mn 2 O 3 , Mn 3 (PO 4 ) 2 , CuO, SnO, SnO 2 , TiO 2 , Ti 2 O 3 , Cr 2 O 3 , PbO 2 , PbO, Ba(OH) 2 , BaO, Cd(OH) 2 .
• Vanadium pentoxide of the formula V 2 O 5 is obtainable from any number of suppliers including Kerr McGee, Johnson Matthey, or Alpha Products of Davers, Mass. Vanadium pentoxide has a CAS number of 1314-62-1. Iron oxide Fe 3 O 3 is a common and very inexpensive material available in powder form from the same suppliers. The other precursor materials mentioned above are also available from well known suppliers, such as those listed above.
• the method of the invention may also be used to react starting materials in the presence of carbon to form a variety of other novel products, such as gamma-LiV 2 O 5 and also to produce known products.
• the carbon functions to reduce metal ion of a starting metal compound to provide a product containing such reduced metal ion.
• the method is particularly useful to also add lithium to the resultant product, which thus contains the metallic element ions, namely, the lithium ion and the other metal ion, thereby forming a mixed metal product.
• An example is the reaction of vanadium pentoxide (V 2 O 5 ) with lithium carbonate in the presence of carbon to form gamma-LiV 2 O 5 .
• the starting metal ion V +5 V +5 is reduced to V +4 V +5 in the final product.
• a single phase gamma-LiV 2 O 5 product is not known to have been directly and independently formed before.
• the temperature should be about 400° C. or greater, and desirably 450° C. or greater, and preferably 500° C. or greater, and generally will proceed at a faster rate at higher temperatures.
• the various reactions involve production of CO or CO 2 as an effluent gas. The equilibrium at higher temperature favors CO formation.
• Some of the reactions are more desirably conducted at temperatures greater than 600° C.; most desirably greater than 650° C.; preferably 700° C. or greater; more preferably 750° C. or greater. Suitable ranges for many reactions are about 700 to 950° C., or about 700 to 800° C.
• the higher temperature reactions produce CO effluent and the stoichiometry requires more carbon be used than the case where CO 2 effluent is produced at lower temperature. This is because the reducing effect of the C to CO 2 reaction is greater than the C to CO reaction.
• the C to CO 2 reaction involves an increase in carbon oxidation state of +4 (from 0 to 4) and the C to CO reaction involves an increase in carbon oxidation state of +2 (from ground state zero to 2).
• higher temperature generally refers to a range of about 650° C. to about 1000° C. and lower temperature refers to up to about 650° C. Temperatures higher than 1200° C. are not thought to be needed.
• the method of the invention utilizes the reducing capabilities of carbon in a unique and controlled manner to produce desired products having structure and lithium content suitable for electrode active materials.
• the method of the invention makes it possible to produce products containing lithium, metal and oxygen in an economical and convenient process.
• the ability to lithiate precursors, and change the oxidation state of a metal without causing abstraction of oxygen from a precursor is heretofore unexpected.
• These advantages are at least in part achieved by the reductant, carbon, having an oxide whose free energy of formation becomes more negative as temperature increases. Such oxide of carbon is more stable at high temperature than at low temperature.
• This feature is used to produce products having one or more metal ions in a reduced oxidation state relative to the precursor metal ion oxidation state.
• the method utilizes an effective combination of quantity of carbon, time and temperature to produce new products and to produce known products in a new way.
• the starting materials are heated at a ramp rate of a fraction of a degree to 10° C. per minute and preferably about 2° C. per minute.
• the reactants starting materials
• the heating is preferably conducted under non-oxidizing or inert gas such as argon or vacuum.
• a reducing atmosphere is not required, although it may be used if desired.
• the products are preferably cooled from the elevated temperature to ambient (room) temperature (i.e., 10° C. to 40° C.).
• the cooling occurs at a rate similar to the earlier ramp rate, and preferably 2° C./minute cooling. Such cooling rate has been found to be adequate to achieve the desired structure of the final product. It is also possible to quench the products at a cooling rate on the order of about 100° C./minute. In some instances, such rapid cooling (quench) may be preferred.
• the present invention resolves the capacity problem posed by widely used cathode active material. It has been found that the capacity and capacity retention of cells having the preferred active material of the invention are improved over conventional materials. Optimized cells containing lithium-mixed metal phosphates of the invention potentially have performance improved over commonly used lithium metal oxide compounds.
• the new method of making the novel lithium-mixed metal phosphate compounds of the invention is relatively economical and readily adaptable to commercial production.
• Objects, features, and advantages of the invention include an electrochemical cell or battery based on lithium-mixed metal phosphates. Another object is to provide an electrode active material which combines the advantages of good discharge capacity and capacity retention. It is also an object of the present invention to provide electrodes which can be manufactured economically. Another object is to provide a method for forming electrode active material which lends itself to commercial scale production for preparation of large quantities.
• FIG. 2 is a voltage/capacity plot of LiFePO 4 -containing cathode cycled with a lithium metal anode using constant current cycling at ⁇ 0.2 milliamps per square centimeter in a range of 2.5 to 4.0 volts at a temperature of about 23° C.
• the cathode contained 19.0 mg of the LiFePO 4 active material, prepared by the method of the invention.
• the electrolyte comprised ethylene carbonate (EC) and dimethyl carbonate (DMC) in a weight ratio of 2:1 and included a 1 molar concentration of LiPF 6 salt.
• the lithium-metal-phosphate containing electrode and the lithium metal counter electrode are maintained spaced apart by a glass fiber separator which is interpenetrated by the solvent and the salt.
• FIG. 3 shows multiple constant current cycling of LiFePO 4 active material cycled with a lithium metal anode using the electrolyte as described in connection with FIG. 2 and cycled, charge and discharge at ⁇ 0.2 milliamps per square centimeter, 2.5 to 4.0 volts at two different temperature conditions, 23° C. and 60° C.
• FIG. 3 shows the excellent rechargeability of the lithium iron phosphate/lithium metal cell, and also shows the excellent cycling and specific capacity (mAh/g) of the active material.
• FIG. 5 is a voltage/capacity plot of LiFe 0.9 Mg 0.1 PO 4 -containing cathode cycled with a lithium metal anode using constant current cycling at ⁇ 0.2 milliamps per square centimeter in a range of 2.5 to 4.0 volts. Other conditions are as described earlier with respect to FIG. 2 .
• the cathode contained 18.9 mg of the LiFe 0.9 Mg 0.1 PO 4 active material prepared by the method of the invention.
• FIG. 6 shows multiple constant current cycling of LiFe 0.9 Mg 0.1 PO 4 cycled with a lithium metal anode using the electrolyte as described in connection with FIG. 2 and cycled, charge and discharge at ⁇ 0.2 milliamps per square centimeter, 2.5 to 4.0 volts at two different temperature conditions, 23° C. and 60° C.
• FIG. 6 shows the excellent rechargeability of the lithium-metal-phosphate/lithium metal cell, and also shows the excellent cycling and capacity of the cell.
• FIG. 7 is a voltage/capacity plot of LiFe 0.8 Mg 0.2 PO 4 -containing cathode cycled with a lithium metal anode using constant current cycling at ⁇ 0.2 milliamps per square centimeter in a range of 2.5 to 4.0 volts at 23° C. Other conditions are as described earlier with respect to FIG. 2 .
• the cathode contained 16 mg of the LiFe 0.8 Mg 0.2 PO 4 active material prepared by the method of the invention.
• FIG. 9 is a voltage/capacity plot of LiFe 0.8 Ca 0.2 PO 4 -containing cathode cycled with a lithium metal anode using constant current cycling at ⁇ 0.2 milliamps per square centimeter in a range of 2.5 to 4.0 volts at 23°. Other conditions are as described earlier with respect to FIG. 2 .
• the cathode contained 18.5 mg of the LiFe 0.8 Ca 0.2 PO 4 active material prepared by the method of the invention.
• FIG. 10 is a voltage/capacity plot of LiFe 0.8 Zn 0.2 PO 4 -containing cathode cycled with a lithium metal anode using constant current cycling at ⁇ 0.2 milliamps per square centimeter in a range of 2.5 to 4.0 volts at 23° C. Other conditions are as described earlier with respect to FIG. 2 .
• the cathode contained 18.9 mg of the LiFe 0.8 Zn 0.2 PO 4 active material prepared by the method of the invention.
• FIG. 12 is a voltage/capacity plot of gamma-LiV 2 O 5 -containing cathode cycled with a lithium metal anode using constant current cycling at ⁇ 0.2 milliamps per square centimeter in a range of 2.5 to 3.8 volts at 23° C. Other conditions are as described earlier with respect to FIG. 2 .
• the cathode contained 21 mg of the gamma-LiV 2 O 5 active material prepared by the method of the invention.
• FIG. 13 is a two-part graph based on multiple constant current cycling of gamma-LiV 2 O 5 cycled with a lithium metal anode using the electrolyte as described in connection with FIG. 2 and cycled, charge and discharge at ⁇ 0.2 milliamps per square centimeter, 2.5 to 3.8 volts.
• FIG. 13 shows the excellent rechargeability of the lithium-metal-oxide/lithium metal cell.
• FIG. 13 shows the excellent cycling and capacity of the cell.
• FIG. 14 shows the results of an x-ray diffraction analysis of the Li 3 V 2 (PO 4 ) 3 prepared according to the invention.
• FIG. 15 shows the results of an x-ray diffraction analysis of Li 3 V 2 (PO 4 ) 3 prepared according to a method described in U.S. Pat. No. 5,871,866.
• FIG. 16 is an EVS (Electrochemical Voltage Spectroscopy) voltage/capacity profile for a cell with cathode material formed by the carbothermal reduction method of the invention.
• the cathode material is 13.8 mg of Li 3 V 2 (PO 4 ) 3 .
• the cell includes a lithium metal counter electrode in an electrolyte comprising ethylene carbonate (EC) and dimethyl carbonate (DMC) in a weight ratio of 2:1 and including a 1 molar concentration of LiPF 6 salt.
• the lithium-metal-phosphate containing electrode and the lithium metal counter electrode are maintained spaced apart by a fiberglass separator which is interpenetrated by the solvent and the salt.
• the conditions are ⁇ 10 mV steps, between about 3.0 and 4.2 volts, and the critical limiting current density is less than or equal to 0.1 mA/cm 2 .
• FIG. 17 is an EVS differential capacity versus voltage plot for the cell as described in connection with FIG. 16 .
• FIG. 18 shows multiple constant current cycling of LiFe 0.8 Mg 0.2 PO 4 cycled with a lithium metal anode using the electrolyte as described in connection with FIG. 2 and cycled, charge and discharge at ⁇ 0.2 milliamps per square centimeter, 2.5 to 4.0 volts at two different temperature conditions, 23° C. and 60° C.
• FIG. 18 shows the excellent rechargeability of the lithium-metal-phosphate/lithium metal cell, and also shows the excellent cycling and capacity of the cell.
• FIG. 19 is a graph of potential over time for the first four complete cycles of the LiMg 0.1 Fe 0.9 PO 4 /MCMB graphite cell of the invention.
• FIG. 20 is a two-part graph based on multiple constant current cycling of LiFe 0.9 Mg 0.1 PO 4 cycled with an MCMB graphite anode using the electrolyte as described in connection with FIG. 2 and cycled, charge and discharge at ⁇ 0.2 milliamps per square centimeter, 2.5 to 3.6 volts, 23° C. and based on a C/10 (10 hour) rate.
• FIG. 20 shows the excellent rechargeability of the lithium-metal-phosphate/graphite cell.
• FIG. 20 shows the excellent cycling and capacity of the cell.
• FIG. 21 is a graph of potential over time for the first three complete cycles of the gamma-LiV 2 O 5 /MCMB graphite cell of the invention.
• FIG. 22 is a diagrammatic representation of a typical laminated lithium-ion battery cell structure.
• FIG. 23 is a diagrammatic representation of a typical multi-cell battery cell structure.
• the present invention provides lithium-mixed metal-phosphates, which are usable as electrode active materials, for lithium (Li + ) ion removal and insertion. Upon extraction of the lithium ions from the lithium-mixed-metal-phosphates, significant capacity is achieved.
• electrochemical energy is provided when combined with a suitable counter electrode by extraction of a quantity x of lithium from lithium-mixed-metal-phosphates Li a-x MI b MII c (PO 4 ) d .
• metal MI is oxidized.
• metal MII is also oxidized.
• At least one of MI and MII is oxidizable from its initial condition in the phosphate compound as Li is removed.
• LiFe 1-y Sn y PO 4 has two oxidizable elements, Fe and Sn; in contrast, LiFe 1-y Mg y PO 4 has one oxidizable metal, the metal Fe.
• the invention provides a lithium ion battery which comprises an electrolyte; a negative electrode having an insertion active material; and a positive electrode comprising a lithium-mixed-metal-phosphate active material characterized by an ability to release lithium ions for insertion into the negative electrode active material.
• the lithium-mixed-metal-phosphate is desirably represented by the nominal general formula Li a MI b MII c (PO 4 ) d .
• the metals MI and MII may be the same, it is preferred that the metals MI and MII are different.
• MI is a metal selected from the group: Fe, Co, Ni, Mn, Cu, V, Sn, Ti, Cr and mixtures thereof, and MI is most desirably a transition metal or mixture thereof selected from said group. Most preferably, MI has a +2 valence or oxidation state.
• MII is selected from Mg, Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be, and mixtures thereof. Most preferably, MII has a +2 valence or oxidation state.
• the lithium-mixed-metal-phosphate is preferably a compound represented by the nominal general formula Li a-x MI b MII c (PO 4 ) d , signifying the preferred composition and its capability to release x lithium. Accordingly, during cycling, charge and discharge, the value of x varies as x greater than or equal to 0 and less than or equal to a.
• the present invention resolves a capacity problem posed by conventional cathode active materials. Such problems with conventional active materials are described by Tarascon in U.S.
• the basic process comprises conducting a reaction between a lithium compound, preferably lithium carbonate (Li 2 CO 3 ), metal compound(s), for example, vanadium pentoxide (V 2 O 5 ), iron oxide (Fe 2 O 3 ), and/or manganese hydroxide, and a phosphoric acid derivative, preferably the phosphoric acid ammonium salt, diammonium hydrogen phosphate, (NH 4 ) 2 H(PO 4 ).
• a lithium compound preferably lithium carbonate (Li 2 CO 3 ), metal compound(s), for example, vanadium pentoxide (V 2 O 5 ), iron oxide (Fe 2 O 3 ), and/or manganese hydroxide
• a phosphoric acid derivative preferably the phosphoric acid ammonium salt, diammonium hydrogen phosphate, (NH 4 ) 2 H(PO 4 ).
• a lithium compound preferably lithium carbonate (Li 2 CO 3 )
• metal compound(s) for example, vanadium pentoxide (V 2 O 5
• LiFePO 4 and LiFe 0.9 Mg 0.1 PO 4 , Li 3 V 2 (PO 4 ) 3 were prepared with approximately a stoichiometric amount of Li 2 CO 3 , the respective metal compound, and (NH 4 ) 2 HPO 4 .
• Carbon powder was included with these precursor materials.
• the precursor materials were initially intimately mixed and dry ground for about 30 minutes.
• the intimately mixed compounds were then pressed into pellets. Reaction was conducted by heating in an oven at a preferred ramped heating rate to an elevated temperature, and held at such elevated temperature for several hours to complete formation of the reaction product.
• the entire reaction was conducted in a non-oxidizing atmosphere, under flowing pure argon gas.
• the flow rate will depend upon the size of the oven and the quantity needed to maintain the atmosphere.
• the oven was permitted to cool down at the end of the reaction period, where cooling occurred at a desired rate under argon.
• Exemplary and preferred ramp rates, elevated reaction temperatures and reaction times are described herein.
• a ramp rate of 2°/minute to an elevated temperature in a range of 750° C. to 800° C. was suitable along with a dwell (reaction time) of 8 hours. Refer to Reactions 1, 2, 3 and 4 herein.
• a reaction temperature of 600° C. was used along with a dwell time of about one hour.
• a two-stage heating was conducted, first to a temperature of 300° C. and then to a temperature of 850°.
• Lithium-containing compounds include Li 2 O (lithium oxide), LiH 2 PO 4 (lithium hydrogen phosphate), Li 2 C 2 O 4 (lithium oxalate), LiOH (lithium hydroxide), LiOH.H 2 O (lithium hydroxide monohydride), and LiHCO 3 (lithium hydrogen carbonate).
• the metal compounds(s) are reduced in the presence of the reducing agent, carbon.
• the same considerations apply to other lithium-metal- and phosphate-containing precursors.
• the thermodynamic considerations such as ease of reduction, of the selected precursors, the reaction kinetics, and the melting point of the salts will cause adjustment in the general procedure, such as, amount of carbon reducing agent, and the temperature of reaction.
• FIGS. 1 through 21 show characterization data and capacity in actual use for the cathode materials (positive electrodes) of the invention. Some tests were conducted in a cell comprising a lithium metal counter electrode (negative electrode) and other tests were conducted in cells having a carbonaceous counter electrode. All of the cells had an EC:DMC-LiPF 6 electrolyte.
• test cells are often fabricated using lithium metal electrodes.
• an insertion positive electrode as per the invention and a graphitic carbon negative electrode.
• a typical laminated battery cell structure 10 is depicted in FIG. 22 . It comprises a negative electrode side 12 , a positive electrode side 14 , and an electrolyte/separator 16 there between. Negative electrode side 12 includes current collector 18 , and positive electrode side 14 includes current collector 22 .
• a copper collector foil 18 preferably in the form of an open mesh grid, upon which is laid a negative electrode membrane 20 comprising an insertion material such as carbon or graphite or low-voltage lithium insertion compound, dispersed in a polymeric binder matrix.
• An electrolyte/separator film 16 membrane is preferably a plasticized copolymer.
• This electrolyte/separator preferably comprises a polymeric separator and a suitable electrolyte for ion transport.
• the electrolyte/separator is positioned upon the electrode element and is covered with a positive electrode membrane 24 comprising a composition of a finely divided lithium insertion compound in a polymeric binder matrix.
• An aluminum collector foil or grid 22 completes the assembly.
• Protective bagging material 40 covers the cell and prevents infiltration of air and moisture.
• a multi-cell battery configuration as per FIG. 23 is prepared with copper current collector 51 , negative electrode 53 , electrolyte/separator 55 , positive electrode 57 , and aluminum current collector 59 .
• Tabs 52 and 58 of the current collector elements form respective terminals for the battery structure.
• the terms “cell” and “battery” refer to an individual cell comprising anode/electrolyte/cathode and also refer to a multi-cell arrangement in a stack.
• the relative weight proportions of the components of the positive electrode are generally: 50–90% by weight active material; 5–30% carbon black as the electric conductive diluent; and 3–20% binder chosen to hold all particulate materials in contact with one another without degrading ionic conductivity. Stated ranges are not critical, and the amount of active material in an electrode may range from 25–95 weight percent.
• the negative electrode comprises about 50–95% by weight of a preferred graphite, with the balance constituted by the binder.
• a typical electrolyte separator film comprises approximately two parts polymer for every one part of a preferred fumed silica.
• the conductive solvent comprises any number of suitable solvents and salts. Desirable solvents and salts are described in U.S. Pat. Nos. 5,643,695 and 5,418,091. One example is a mixture of EC:DMC:LiPF 6 in a weight ratio of about 60:30:10.
• Solvents are selected to be used individually or in mixtures, and include dimethyl carbonate (DMC), diethylcarbonate (DEC), dipropylcarbonate (DPC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, lactones, esters, glymes, sulfoxides, sulfolanes, etc.
• the preferred solvents are EC/DMC, EC/DEC, EC/DPC and EC/EMC.
• the salt content ranges from 5% to 65% by weight, preferably from 8% to 35% by weight.
• any number of methods are used to form films from the casting solution using conventional meter bar or doctor blade apparatus. It is usually sufficient to air-dry the films at moderate temperature to yield self-supporting films of copolymer composition.
• Lamination of assembled cell structures is accomplished by conventional means by pressing between metal plates at a temperature of about 120–160° C. Subsequent to lamination, the battery cell material may be stored either with the retained plasticizer or as a dry sheet after extraction of the plasticizer with a selective low-boiling point solvent.
• the plasticizer extraction solvent is not critical, and methanol or ether are often used.
• Separator membrane element 16 is generally polymeric and prepared from a composition comprising a copolymer.
• a preferred composition is the 75 to 92% vinylidene fluoride with 8 to 25% hexafluoropropylene copolymer (available commercially from Atochem North America as Kynar FLEX) and an organic solvent plasticizer.
• the plasticizing solvent may be one of the various organic compounds commonly used as solvents for electrolyte salts, e.g., propylene carbonate or ethylene carbonate, as well as mixtures of these compounds.
• Higher-boiling plasticizer compounds such as dibutyl phthalate, dimethyl phthalate, diethyl phthalate, and tris butoxyethyl phosphate are particularly suitable.
• Inorganic filler adjuncts such as fumed alumina or silanized fumed silica, may be used to enhance the physical strength and melt viscosity of a separator membrane and, in some compositions, to increase the subsequent level of electrolyte solution absorption.
• a current collector layer of aluminum foil or grid is overlaid with a positive electrode film, or membrane, separately prepared as a coated layer of a dispersion of insertion electrode composition.
• This is typically an insertion compound such as LiMn 2 O 4 (LMO), LiCoO 2 , or LiNiO 2 , powder in a copolymer matrix solution, which is dried to form the positive electrode.
• An electrolyte/separator membrane is formed as a dried coating of a composition comprising a solution containing VdF:HFP copolymer and a plasticizer solvent is then overlaid on the positive electrode film.
• a negative electrode membrane formed as a dried coating of a powdered carbon or other negative electrode material dispersion in a VdF:HFP copolymer matrix solution is similarly overlaid on the separator membrane layer.
• a copper current collector foil or grid is laid upon the negative electrode layer to complete the cell assembly. Therefore, the VdF:HFP copolymer composition is used as a binder in all of the major cell components, positive electrode film, negative electrode film, and electrolyte/separator membrane.
• the assembled components are then heated under pressure to achieve heat-fusion bonding between the plasticized copolymer matrix electrode and electrolyte components, and to the collector grids, to thereby form an effective laminate of cell elements. This produces an essentially unitary and flexible battery cell structure.
• VdF:HFP polymeric matrix More modern examples are the VdF:HFP polymeric matrix. Examples of casting, lamination and formation of cells using VdF:HFP are as described in U.S. Pat. Nos. 5,418,091; 5,460,904; 5,456,000; and 5,540,741; assigned to Bell Communications Research, each of which is incorporated herein by reference in its entirety.
• the electrochemical cell operated as per the invention may be prepared in a variety of ways.
• the negative electrode may be metallic lithium.
• the negative electrode is an insertion active material, such as, metal oxides and graphite.
• the components of the electrode are the metal oxide, electrically conductive carbon, and binder, in proportions similar to that described above for the positive electrode.
• the negative electrode active material is graphite particles.
• test cells are often fabricated using lithium metal electrodes. When forming cells for use as batteries, it is preferred to use an insertion metal oxide positive electrode and a graphitic carbon negative electrode.
• Various methods for fabricating electrochemical cells and batteries and for forming electrode components are described herein. The invention is not, however, limited by any particular fabrication method.
• LiFePO 4 formed from FePO 4 FePO 4 +0.5 Li 2 CO 3 +0.5 C ⁇ LiFePO 4 +0.5 CO 2+ 0.5 CO
• LiFePO 4 formed from Fe 2 O 3 0.5 Fe 2 O 3 +0.5 Li 2 CO 3 +(NH 4 ) 2 HPO 4 +0.5 C ⁇ LiFePO 4 +0.5 CO 2 +2 NH 3 +3/2 H 2 O+0.5 CO
• LiFe 0.9 Mg 0.1 PO 4 LiFe 1-y Mg y PO 4 formed from FePO 4 0.5 Li 2 CO 3 +0.9 FePO 4 +0.1 Mg(OH) 2 +0.1(NH 4 ) 2 HPO 4 +0.45C ⁇ LiFe 0.9 Mg 0.1 PO 4 +0.5CO 2 +0.45CO+0.2NH 3 +0.25 H 2 O
• LiFe 0.9 Mg 0.1 PO 4 LiFe 1-y Mg y PO 4 formed from Fe 2 O 3 0.50 Li 2 CO 3 +0.45 Fe 2 O 3 +0.10 Mg (OH) 2 +(NH 4 ) 2 HPO 4 +0.45C ⁇ LiFe 0.9 Mg 0.1 PO 4 +0.5 CO 2 +0.45 CO+2 NH 3 +1.6 H 2 O
• LiFe 0.9 Mg 0.1 PO 4 LiFe 1-y Mg y PO 4 formed from LiH 2 PO 4 1.0 LiH 2 PO 4 +0.45 Fe 2 O 3 +0.10 Mg(OH) 2 +0.45C ⁇ LiFe 0.9 Mg 0.1 PO 4 +0.45 CO+1.1 H 2 O
• Reaction 4 Formation of LiFe 0.9 Zn 0.1 PO 4 (LiFe 1-y Zn y PO 4 ) from Fe 2 O 3 . 0.50 Li 2 CO 3 +0.45 Fe 2 O 3 +0.033 Zn 3 (PO 4 ) 2 +0.933(NH 4 ) 2 HPO 4 +0.45 C ⁇ LiFe 0.9 Zn 0.1 PO 4 +0.50 CO 2 +0.45 CO+1.866 NH 3 +1.2H 2 O
• This reaction is able to be conducted at a temperature in a range of about 400° C. to about 650° C. in argon as shown, and also under other inert atmospheres such as nitrogen or vacuum.
• This reaction at this temperature range is primarily C ⁇ CO 2 .
• the reaction C ⁇ CO primarily occurs at a temperature over about 650° C. (HT, high temperature); and the reaction C ⁇ CO 2 primarily occurs at a temperature of under about 650° C. (LT, low temperature).
• the reference to about 650° C. is approximate and the designation “primarily” refers to the predominant reaction thermodynamically favored although the alternate reaction may occur to some extent.
• This reaction is able to be conducted at a temperature in a range of about 700° C. to about 950° C. in argon as shown, and also under other inert atmospheres such as nitrogen or vacuum.
• a reaction temperature greater than about 670° C. ensures C ⁇ CO reaction is primarily carried out.
• the final product LiFePO 4 prepared from Fe 2 O 3 metal compound per Reaction 1(b), appeared brown/black in color.
• This olivine material product included carbon that remained after reaction. Its CuK ⁇ x-ray diffraction pattern contained all of the peaks expected for this material as shown in FIG. 1 .
• the pattern evident in FIG. 1 is consistent with the single phase olivine phosphate, LiFePO 4 . This is evidenced by the position of the peaks in terms of the scattering angle 2 ⁇ (theta), x axis.
• the x-ray pattern showed no peaks due to the presence of precursor oxides indicating that the solid state reaction is essentially entirely completed.
• nominal formula refers to the fact that the relative proportion of atomic species may vary slightly on the order of 2 percent to 5 percent, or more typically, 1 percent to 3 percent, and that some portion of P may be substituted by Si, S or As; and some portion of O may be substituted by halogen, preferably F.
• the LiFePO 4 prepared as described immediately above, was tested in an electrochemical cell.
• the positive electrode was prepared as described above, using 19.0 mg of active material.
• the positive electrode contained, on a weight % basis, 85% active material, 10% carbon black, and 5% EPDM.
• the negative electrode was metallic lithium.
• the electrolyte was a 2:1 weight ratio mixture of ethylene carbonate and dimethyl carbonate within which was dissolved 1 molar LiPF 6 .
• the cells were cycled between about 2.5 and about 4.0 volts with performance as shown in FIGS. 2 and 3 .
• FIG. 2 shows the results of the first constant current cycling at 0.2 milliamps per square centimeter between about 2.5 and 4.0 volts based upon about 19 milligrams of the LiFePO 4 active material in the cathode (positive electrode).
• the positive electrode active material is LiFePO 4 .
• the lithium is extracted from the LiFePO 4 during charging of the cell.
• about 0.72 unit of lithium had been removed per formula unit. Consequently, the positive electrode active material corresponds to Li 1-x FePO 4 where x appears to be equal to about 0.72, when the cathode material is at 4.0 volts versus Li/Li + .
• the extraction represents approximately 123 milliamp hours per gram corresponding to about 2.3 milliamp hours based on 19 milligrams active material.
• the cell is discharged whereupon a quantity of lithium is re-inserted into the LiFePO 4 .
• the re-insertion corresponds to approximately 121 milliamp hours per gram proportional to the insertion of essentially all of the lithium.
• the bottom of the curve corresponds to approximately 2.5 volts.
• the total cumulative capacity demonstrated during the entire extraction-insertion cycle is 244 mAh/g.
• FIG. 3 presents data obtained by multiple constant current cycling at 0.2 milliamp hours per square centimeter of the LiFePO 4 versus lithium metal counter electrode between 2.5 and 4.0 volts. Data is shown for two temperatures, 23° C. and 60° C.
• FIG. 3 shows the excellent rechargeability of the LiFePO 4 cell, and also shows good cycling and capacity of the cell. The performance shown after about 190 to 200 cycles is good and shows that electrode formulation is very desirable.
• FIG. 4 there is shown data for the final product LiFe 0.9 Mg 0.1 PO 4 , prepared from the metal compounds Fe 2 O 3 and Mg(OH) 2 ⁇ Mg(OH) 2 , per Reaction 2(b). Its CuK ⁇ x-ray diffraction pattern contained all of the peaks expected for this material as shown in FIG. 4 .
• the pattern evident in FIG. 4 is consistent with the single phase olivine phosphate compound, LiFe 0.9 Mg 0.1 PO 4 . This is evidenced by the position of the peaks in terms of the scattering angle 2 ⁇ (theta), x axis.
• the x-ray pattern showed no peaks due to the presence of precursor oxides indicating that the solid state reaction is essentially entirely completed.
• the x-ray pattern demonstrates that the product of the invention was indeed the nominal formula LiFe 0.9 Mg 0.1 PO 4
• nominal formula refers to the fact that the relative proportion of atomic species may vary slightly on the order of 2 percent to 5 percent, or more typically, 1 percent to 3 percent, and that some substitution of P and O may be made while maintaining the basic olivine structure.
• the LiFe 0.9 Mg 0.1 PO 4 prepared as described immediately above, was tested in an electrochemical cell.
• the positive electrode was prepared as described above, using 18.9 mg of active materials.
• the positive electrode, negative electrode and electrolyte were prepared as described earlier and in connection with FIG. 1 .
• the cell was between about 2.5 and about 4.0 volts with performance as shown in FIGS. 4 , 5 and 6 .
• FIG. 5 shows the results of the first constant current cycling at 0.2 milliamps per square centimeter between about 2.5 and 4.0 volts based upon about 18.9 milligrams of the LiFe 0.9 Mg 0.1 PO 4 active material in the cathode (positive electrode).
• the positive electrode active material is LiFe 0.9 Mg 0.1 PO 4 .
• the lithium is extracted from the LiFe 0.9 Mg 0.1 PO 4 during charging of the cell. When fully charged, about 0.87 units of lithium have been removed per formula unit.
• the positive electrode active material corresponds to Li 1-x Fe 0.9 Mg 0.1 PO 4 where x appears to be equal to about 0.87, when the cathode material is at 4.0 volts versus Li/Li + .
• the extraction represents approximately 150 milliamp hours per gram corresponding to about 2.8 milliamp hours based on 18.9 milligrams active material.
• the cell is discharged whereupon a quantity of lithium is re-inserted into the LiFe 0.9 Mg 0.1 PO 4 .
• the re-insertion corresponds to approximately 146 milliamp hours per gram proportional to the insertion of essentially all of the lithium.
• the bottom of the curve corresponds to approximately 2.5 volts.
• the total cumulative specific capacity over the entire cycle is 296 mAhr/g.
• FIG. 5 LiFe 0.9 Mg 0.1 PO 4
• FIG. 2 LiFePO 4
• FIG. 5 shows a very well defined and sharp peak at about 150 mAh/g.
• FIG. 2 shows a very shallow slope leading to the peak at about 123 mAh/g.
• the Fe-phosphate FIG. 2
• the Fe/Mg-phosphate FIG. 5
• the Fe/Mg-phosphate FIG. 5
• the Fe/Mg-phosphate provides 150 mAh/g compared to a theoretical capacity of 160, a ratio of 150/160 or 94%.
• FIG. 6 presents data obtained by multiple constant current cycling at 0.2 milliamp hours per square centimeter of the LiFe 0.9 Mg 0.1 PO 4 versus lithium metal counter electrode between 2.5 and 4.0 volts.
• FIG. 6 shows the excellent rechargeability of the Li/LiFe 0.9 Mg 0.1 PO 4 cell, and also shows good cycling and capacity of the cell. The performance shown after about 150 to 160 cycles is very good and shows that electrode formulation LiFe 0.9 Mg 0.1 PO 4 performed significantly better than the LiFePO 4 . Comparing FIG. 3 (LiFePO 4 ) to FIG. 6 (LiFe 0.9 Mg 0.1 PO 4 ) it can be seen that the Fe/Mg-phosphate maintains its capacity over prolonged cycling, whereas the Fe-phosphate capacity fades significantly.
• FIG. 7 shows the results of the first constant current cycling at 0.2 milliamps per square centimeter between about 2.5 and 4.0 volts based upon about 16 milligrams of the LiFe 0.8 Mg 0.2 PO 4 active material in the cathode (positive electrode).
• the positive electrode active material is LiFe 0.8 Mg 0.2 PO 4 .
• the lithium is extracted from the LiFe 0.8 Mg 0.2 PO 4 during charging of the cell. When fully charged, about 0.79 units of lithium have been removed per formula unit.
• the positive electrode active material corresponds to LiFe 0.8 Mg 0.2 PO 4 where x appears to be equal to about 0.79, when the cathode material is at 4.0 volts versus Li/Li + .
• the extraction approximately 135 milliamp hours per gram corresponding to about 2.2 milliamp hours based on 16 milligrams active material.
• the cell is discharged whereupon a quantity of lithium is re-inserted into the LiFe 0.8 Mg 0.2 PO 4 .
• the re-insertion corresponds to approximately 122 milliamp hours per gram proportional to the insertion of essentially all of the lithium.
• the bottom of the curve corresponds to approximately 2.5 volts.
• the total cumulative specific capacity over the entire cycle is 262 mAhr/g.
• FIG. 8 there is shown data for the final product LiFe 0.9 Ca 0.1 PO 4 , prepared from Fe 2 O 3 and Ca(OH) 2 by Reaction 3. Its CuK ⁇ x-ray diffraction pattern contained all of the peaks expected for this material as shown in FIG. 8 .
• the pattern evident in FIG. 8 is consistent with the single phase olivine phosphate compound, LiFe 0.9 Ca 0.1 PO 4 . This is evidenced by the position of the peaks in terms of the scattering angle 2 ⁇ (theta), x axis.
• the x-ray pattern showed no peaks due to the presence of precursor oxides indicating that the solid state reaction is essentially entirely completed.
• FIG. 9 shows the results of the first constant current cycling at 0.2 milliamps per square centimeter between about 2.5 and 4.0 volts based upon about 18.5 milligrams of the LiFe 0.8 Ca 0.2 PO 4 active material in the cathode (positive electrode).
• the positive electrode active material is LiFe 0.8 Ca 0.2 PO 4 .
• the lithium is extracted from the LiFe 0.8 Ca 0.2 PO 4 during charging of the cell.
• about 0.71 units of lithium have been removed per formula unit. Consequently, the positive electrode active material corresponds to LiFe 0.8 Ca 0.2 PO 4 where x appears to be equal to about 0.71, when the cathode material is at 4.0 volts versus Li/Li + .
• the extraction represents approximately 123 milliamp hours per gram corresponding to about 2.3 milliamp hours based on 18.5 milligrams active material.
• the cell is discharged whereupon a quantity of lithium is re-inserted into the LiFe 0.8 Ca 0.2 PO 4 .
• the re-insertion corresponds to approximately 110 milliamp hours per gram proportional to the insertion of nearly all of the lithium.
• the bottom of the curve corresponds to approximately 2.5 volts.
• the total specific cumulative capacity over the entire cycle is 233 mAhr/g.
• FIG. 10 shows the results of the first constant current cycling at 0.2 milliamps per square centimeter between about 2.5 and 4.0 volts based upon about 18.9 milligrams of the LiFe 0.8 Zn 0.2 PO 4 olivine active material in the cathode (positive electrode).
• the positive electrode active material is LiFe 0.8 Zn 0.2 PO 4 , prepared from Fe 2 O 3 and Zn 3 (PO 4 ) 2 by Reaction 4.
• the lithium is extracted from the LiFe 0.8 Zn 0.2 PO 4 during charging of the cell. When fully charged, about 0.74 units of lithium have been removed per formula unit.
• the positive electrode active material corresponds to Li 1-x Fe0.8Zn0.2PO4 where x appears to be equal to about 0.74, when the cathode material is at 4.0 volts versus Li/Li + .
• the extraction represents approximately 124 milliamp hours per gram corresponding to about 2.3 milliamp hours based on 18.9 milligrams active material.
• the cell is discharged whereupon a quantity of lithium is re-inserted into the LiFe 0.8 Zn 0.2 PO 4 .
• the re-insertion corresponds to approximately 108 milliamp hours per gram proportional to the insertion of nearly all of the lithium.
• the bottom of the curve corresponds to approximately 2.5 volts.
• the final product LiV 2 O 5 prepared by Reaction 5, appeared black in color. Its CuK ⁇ x-ray diffraction pattern contained all of the peaks expected for this material as shown in FIG. 11 .
• the pattern evident in FIG. 11 is consistent with a single oxide compound gamma-LiV 2 O 5 This is evidenced by the position of the peaks in terms of the scattering angle 2 ⁇ (theta), x axis.
• the x-ray pattern showed no peaks due to the presence of precursor oxides indicating that the solid state reaction is essentially entirely completed.
• the x-ray pattern demonstrates that the product of the invention was indeed the nominal formula gamma-LiV 2 O 5 .
• nominal formula refers to the fact that the relative proportion of atomic species may vary slightly on the order of 2 percent to 5 percent, or more typically, 1 percent to 3 percent.
• the cell was prepared as described above and cycled with performance as shown in FIGS. 12 and 13 .
• FIG. 12 shows the results of the first constant current cycling at 0.2 milliamps per square centimeter between about 2.8 and 3.8 volts based upon about 15.0 milligrams of the LiV 2 O 5 active material in the cathode (positive electrode).
• the positive electrode active material is LiV 2 O 5 .
• the lithium is extracted from the LiV 2 O 5 during charging of the cell.
• about 0.93 unit of lithium had been removed per formula unit. Consequently, the positive electrode active material corresponds to Li 1-x -V 2 O 5 where x appears to be equal to about 0.93, when the cathode material is at 3.8 volts versus Li/Li + .
• the extraction represents approximately 132 milliamp hours per gram corresponding to about 2.0 milliamp hours based on 15.0 milligrams active material.
• the cell is discharged whereupon a quantity of lithium is re-inserted into the LiV 2 O 5 .
• the re-insertion corresponds to approximately 130 milliamp hours per gram proportional to the insertion of essentially all of the lithium.
• the bottom of the curve corresponds to approximately 2.8 volts.
• FIG. 13 presents data obtained by multiple constant current cycling at 0.4 milliamp hours per square centimeter (C/2 rate)of the LiV 2 O 5 versus lithium metal counter electrode between 3.0 and 3.75 volts. Data for two temperature conditions are shown, 23° C. and 60° C.
• FIG. 13 is a two part graph with FIG. 13A showing the excellent rechargeability of the LiV 2 O 5 .
• FIG. 13B shows good cycling and capacity of the cell. The performance shown up to about 300 cycles is good.
• the final product Li 3 V 2 (PO 4 ) 3 prepared by Reaction 6, appeared green/black in color. Its CuK ⁇ x-ray diffraction pattern contained all of the peaks expected for this material as shown in FIG. 14 .
• the pattern evident in FIG. 14 is consistent with a single phosphate compound Li 3 V 2 (PO 4 ) 3 of the monoclinic, Nasicon phase. This is evidenced by the position of the peaks in terms of the scattering angle 2 ⁇ (theta), x axis.
• the x-ray pattern showed no peaks due to the presence of precursor oxides indicating that the solid state reaction is essentially entirely completed.
• the x-ray pattern demonstrates that the product of the invention was indeed the nominal formula Li 3 V 2 (PO 4 ) 3 .
• nominal formula refers to the fact that the relative proportion of atomic species may vary slightly on the order of 2 percent to 5 percent, or more typically, 1 percent to 3 percent; and that substitution of P and O may occur.
• FIG. 16 shows specific capacity versus electrode potential against Li.
• FIG. 17 shows differential capacity versus electrode potential against Li.
• a comparative method was used to form Li 3 V 2 (PO 4 ) 3 .
• Such method was reaction without carbon and under H 2 -reducing gas as described in U.S. Pat. No. 5,871,866.
• Its CuK ⁇ x-ray diffraction pattern contained all of the peaks expected for this material as shown in FIG. 15 .
• the pattern evident in FIG. 15 is consistent with a monoclinic Nasicon single phase phosphate compound Li 3 V 2 (PO 4 ) 3 . This is evidenced by the position of the peaks in terms of the scattering angle 2 ⁇ (theta), x axis.
• FIGS. 14 and 15 demonstrate that the product of FIG. 14 was the same as that of FIG. 15 .
• the product of FIG. 14 was prepared without the undesirable H 2 atmosphere and was prepared by the novel carbothermal solid state synthesis of the invention.
• FIG. 16 shows a voltage profile of the test cell, based on the Li 3 V 2 (PO 4 ) 3 positive electrode active material made by the process of the invention and as characterized in FIG. 14 . It was cycled against a lithium metal counter electrode.
• the data shown in FIG. 16 is based on the Electrochemical Voltage Spectroscopy (EVS) technique. Electrochemical and kinetic data were recorded using the Electrochemical Voltage Spectroscopy (EVS) technique.
• EVS Electrochemical Voltage Spectroscopy
• FIG. 16 clearly shows and highlights the reversibility of the product.
• the positive electrode contained about 13.8 milligrams of the Li 3 V 2 (PO 4 ) 3 active material.
• the positive electrode showed a performance of about 133 milliamp hours per gram on the first discharge.
• FIG. 16 the capacity in, and the capacity out are essentially the same, resulting in essentially no capacity loss.
• FIG. 17 is an EVS differential capacity plot based on FIG. 16 . As can be seen from FIG. 17 , the relatively symmetrical nature of peaks indicates good electrical reversibility, there are small peak separations (charge/discharge), and good correspondence between peaks above and below the zero axis.
• FIG. 18 presents data obtained by multiple constant current cycling at 0.2 milliamp hours per square centimeter of the LiFe 0.8 Mg 0.2 PO 4 versus lithium metal counter electrode between 2.5 and 4.0 volts.
• FIG. 18 shows the excellent rechargeability of the Li/LiFe 0.8 Mg 0.2 PO 4 cell, and also shows good cycling and capacity of the cell. The performance shown after about 110 to 120 cycles at 23° C. is very good and shows that electrode formulation LiFe 0.8 Mg 0.2 PO 4 performed significantly better than the LiFePO 4 .
• the cell cycling test at 60° C. was started after the 23° C. test and was ongoing. Comparing FIG. 3 (LiFePO 4 ) to FIG. 18 (LiFe 0.8 Mg 0.2 PO 4 ), it can be seen that the Fe/Mg-phosphate maintains its capacity over prolonged cycling, whereas the Fe-phosphate capacity fades significantly.
• the active materials of the invention were also cycled against insertion anodes in non-metallic, lithium ion, rocking chair cells.
• the lithium mixed metal phosphate and the lithium metal oxide were used to formulate a cathode electrode.
• the electrode was fabricated by solvent casting a slurry of the treated, enriched lithium manganese oxide, conductive carbon, binder, plasticizer and solvent.
• the conductive carbon used was Super P (MMM Carbon).
• Kynar Flex 2801® was used as the binder and electronic grade acetone was used as a solvent.
• the preferred plasticizer was dibutyl phthalate (DPB).
• the slurry was cast onto glass and a free-standing electrode was formed as the solvent was evaporated.
• the cathode had 23.1 mg LiFe 0.9 Mg 0.1 PO 4 active material.
• the proportions are as follows on a percent weight basis: 80% active material; 8% Super P carbon; and 12% Kynar binder.
• a graphite counter electrode was prepared for use with the aforesaid cathode.
• the graphite counter electrode served as the anode in the electrochemical cell.
• the anode had 10.8 mg of the MCMB graphite active material.
• the graphite electrode was fabricated by solvent casting a slurry of MCMB2528 graphite, binder, and casting solvent.
• MCMB2528 is a mesocarbon microbead material supplied by Alumina Trading, which is the U.S. distributor for the supplier, Osaka Gas Company of Japan.
• This material has a density of about 2.24 grams per cubic centimeter; a particle size maximum for at least 95% by weight of the particles of 37 microns; median size of about 22.5 microns and an interlayer distance of about 0.336.
• the binder was a copolymer of polyvinylidene difluoride (PVdF) and hexafluoropropylene (HFP) in a wt. ratio of PVdF to HFP of 88:12.
• PVdF polyvinylidene difluoride
• HFP hexafluoropropylene
• This binder is sold under the designation of Kynar Flex 2801®, showing it's a registered trademark. Kynar Flex is available from Atochem Corporation.
• An electronic grade solvent was used. The slurry was cast onto glass and a free standing electrode was formed as the casting solvent evaporated.
• the electrode composition was approximately as follows on a dry weight basis: 85% graphite; 12% binder; and 3%
• a rocking chair battery was prepared comprising the anode, the cathode, and an electrolyte.
• the ratio of the active cathode mass to the active anode mass was about 2.14:1.
• the two electrode layers were arranged with an electrolyte layer in between, and the layers were laminated together using heat and pressure as per the Bell Comm. Res. patents incorporated herein by reference earlier.
• the cell is activated with EC/DMC solvent in a weight ratio of 2:1 in a solution containing 1 M LiPF 6 salt.
• FIGS. 19 and 20 show data for the first four complete cycles of the lithium ion cell having the LiFe 0.9 Mg 0.1 PO 4 cathode and the MCMB2528 anode.
• the cell comprised 23.1 mg active LiFe 0.9 Mg 0.1 P 4 and 10.8 mg active MCMB2528 for a cathode to anode mass ratio of 2.14.
• the cell was charged and discharged at 23° C. at an approximate C/10 (10 hour) rate between voltage limits of 2.50 V and 3.60 V.
• the voltage profile plot ( FIG. 19 ) shows the variation in cell voltage versus time for the LiFe 0.9 Mg 0.1 PO 4 /MCMB2528 lithium ion cell. The symmetrical nature of the charge-discharge is clearly evident.
• FIG. 20 shows the variation of LiFe 0.9 Mg 0.1 PO 4 specific capacity with cycle number. Clearly, over the cycles shown, the material demonstrates good cycling stability.
• FIG. 21 shows data for the first three complete cycles of the lithium ion cell having the gamma-LiV 2 O 5 cathode and the MCMB2528 anode.
• the cell prepared was a rocking chair, lithium ion cell as described above.
• the cell comprised 29.1 mg gamma-LiV 2 O 5 cathode active material and 12.2 mg MCMB2528 anode active material, for a cathode to anode mass ratio of 2.39.
• the liquid electrolyte used was EC/DMC (2:1) and 1M LiPF 6 .
• the cell was charged and discharged at 23° C. at an approximate C/10 (10 hour) rate between voltage limits of 2.50 V and 3.65 V.
• the voltage profile plot ( FIG.
• the invention provides new compounds Li a MI b MII c (PO 4 ) d and gamma-LiV 2 O 5 by new methods which are adaptable to commercial scale production.
• the Li 1 MI 1-y MII y PO 4 compounds are isostructural olivine compounds as demonstrated by XRD analysis.
• Substituted compounds, such as LiFe 1-y Mg y PO 4 show better performance than LiFePO 4 unsubstituted compounds when used as electrode active materials.
• the method of the invention utilizes the reducing capabilities of carbon along with selected precursors and reaction conditions to produce high quality products suitable as electrode active materials or as ion conductors.
• the reduction capability of carbon over a broad temperature range is selectively applied along with thermodynamic and kinetic considerations to provide an energy-efficient, economical and convenient process to produce compounds of a desired composition and structure. This is in contrast to known methods.
• alpha-V 2 O 5 is conventionally lithiated electrochemically against metallic lithium.
• alpha-V 2 O 5 is not suitable as a source of lithium for a cell.
• alpha-V 2 O 5 is not used in an ion cell.
• alpha-V 2 O 5 is lithiated by carbothermal reduction using a simple lithium-containing compound and the reducing capability of carbon to form a gamma-LiV 2 O 5 .
• the single phase compound, gamma-LiV 2 O 5 is not known to have been directly and independently prepared before. There is not known to be a direct synthesis route.
• atomic unit of carbon is used to reduce one atomic unit of vanadium, that is, V +5 V +5 to V +5 V +4 .
• the predominate reaction is C to CO 2 where for each atomic unit of carbon at ground state zero, a plus 4 oxidation state results.
• one atomic unit of vanadium is reduced from V +5 to V +4 . (See Reaction 5).
• the new product, gamma-LiV 2 O 5 is air-stable and suitable as an electrode material for an ion cell or rocking chair battery.
• LiFePO 4 is the reducing agent, and simple, inexpensive and even naturally occurring precursors are useable.
• LiFePO 4 is the reducing agent, and simple, inexpensive and even naturally occurring precursors are useable.
• the production of LiFePO 4 provides a good example of the thermodynamic and kinetic features of the method. Iron phosphate is reduced by carbon and lithiated over a broad temperature range. At about 600° C., the C to CO 2 reaction predominates and takes about a week to complete.
• the C to CO reaction predominates and takes about 8 hours to complete.
• the C to CO 2 reaction requires less carbon reductant but takes longer due to the low temperature kinetics.
• the C to CO reaction requires about twice as much carbon, but due to the high temperature reaction kinetics, it proceeds relatively fast.
• the Fe in the precursor Fe 2 O 3 has oxidation state +3 and is reduced to oxidation (valence) state +2 in the product LiFePO 4 .
• the C to CO reaction requires that 1 ⁇ 2 atomic unit of carbon be used for each atomic unit of Fe reduced by one valence state.
• the CO to CO 2 reaction requires that 1 ⁇ 4 atomic unit of carbon be used for each atomic unit of Fe reduced by one valence state.
• the active materials of the invention are also characterized by being stable in an as-prepared condition, in the presence of air and particularly humid air. This is a striking advantage, because it facilitates preparation of and assembly of battery cathodes and cells, without the requirement for controlled atmosphere. This feature is particularly important, as those skilled in the art will recognize that air stability, that is, lack of degradation on exposure to air, is very important for commercial processing. Air-stability is known in the art to more specifically indicate that a material does not hydrolyze in presence of moist air. Generally, air-stable materials are also characterized by Li being extracted therefrom above about 3.0 volts versus lithium. The higher the extraction potential, the more tightly bound the lithium ions are to the host lattice. This tightly bound property generally confers air stability on the material.
• the air-stability of the materials of the invention is consistent with the stability demonstrated by cycling at the conditions stated herein. This is in contrast to materials which insert Li at lower voltages, below about 3.0 volts versus lithium, and which are not air-stable, and which hydrolyze in moist air.

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